To pass cooling air through a heat exchanger, such as a vehicle radiator, an axial flow fan is often used. The fan may be disposed upstream of the heat exchanger, such that air is blown through the heat exchanger, or downstream, such that air is drawn through the heat exchanger by the fan. Where air is blown through the heat exchanger by the fan, the air pressure in the region between the fan and the heat exchanger is raised by the action of the fan, and on the side of the fan remote from the heat exchanger, the air pressure is lowered. The reverse situation applies where air is drawn by the fan. There is accordingly a tendency for air to flow directly around the axial periphery of the fan between the high pressure region and the low pressure region. This air circulation, called reflux of air and causing so-called "tip vortices", however does not provide any cooling benefits.
Recently much interest has centered around the provision of a so-called "shroud" extending axially from the fan to at least a portion of the heat exchanger. The shroud is stationary and has a portion which houses the circumferential periphery of the fan. One function of such a shroud is to funnel air from the heat exchanger to the fan; another is to reduce the area of any reflux path around the fan. A problem in some applications is that the shroud increases the complexity of, and also adds to the weight of the cooling arrangement. Furthermore the acoustic properties of a shroud may cause resonances to occur and this is undesirable.
It is also known to provide axial flow fans with a so-called "tip support ring", in the form of a rotating cylindrical band disposed at, and joining together, the tips of the plural blades of the fan. The tip support ring provides additional stiffness to the fan and accordingly provides more predictable fan properties and dimensions. The ring may be used in cooperation with the stationary shroud to provide further restriction of the area for reflux flow around the fan.